1. A Doppler decoy protection device comprising a missile capable of being launched from a space craft whose protection is sought, and to travel in advance thereof and at a speed greater than the speed of said space craft, guide means extendable rearwardly from said missile, Doppler decoy means slidable on said guide means for simulating the Doppler characteristics of the craft whose protection is sought, means for damping the speed of travel of said decoy means rearwardly on said guide means so that the resultant forward speed of said decoy means will substantially equal the speed of the craft whose protection is sought.